Field of the Invention
The present invention relates to a substrate processing apparatus and a substrate processing method which are useful for performing processing using a liquid (processing liquid), such as plating, pre-plating treatment, electrolytic etching, etc. on a surface of a substrate such as a semiconductor wafer.
Description of the Related Art
Metal plating, such as copper plating, has recently been employed as a method to fill a metal (interconnect material) into fine interconnect trenches or vias provided in a surface of a substrate, such as a semiconductor wafer. Metal plating has come to be commonly used also as a method to form protruding connection electrodes (bumps) of gold, copper, solder or nickel, or of a multi-layer laminate of such metals at predetermined positions (electrodes) on a surface of a semiconductor chip on which interconnects are formed.
When filling a metal (plated film) into fine interconnect trenches or vias, provided in a surface of a substrate, by metal plating, the intensity of a flow of a plating solution, flowing along the surface of the substrate, is of importance. Adsorption of an additive, contained in the plating solution, onto the substrate surface (surface to be plated) is affected by the intensity of a flow of the plating solution flowing along the surface of the substrate. The intensity of the flow of the plating solution therefore affects the effect of the additive, e.g., inhibition or promotion of the growth of a plated film. Further, a non-uniform flow of the plating solution along the surface adversely affects the uniformity of the performance of plating. A technique for allowing a plating solution to flow uniformly parallel to a substrate has been developed to obtain a uniform distribution of the flow of the plating solution along the surface of the substrate (see patent documents 1 and 2).
Because of the consumption of an additive or a metal ion in a plating solution, a difference in the plating performance can be produced between the upstream side and the downstream side of a flow of the plating solution along a substrate surface even when the flow is uniform over the substrate surface. In view of this, a method has been proposed which involves reversing the direction of a flow of a plating solution repeatedly during plating (patent documents 3 to 5).
Thus, it is progressing to improve the equalization of a flow of a plating solution along a substrate surface. It is also important to equalize (flatten) the surface profile of a metal (plated film) embedded in fine interconnect trenches or vias, or bumps formed at predetermined positions on a surface of a semiconductor chip. For example, in the formation of a bump by electroplating as performed by preparing a substrate W, having an opening 14 formed in a resist 12 on a surface of a seed layer 10, as shown in FIG. 1A, and bringing the surface of the substrate W into contact with a plating solution flowing only in one direction, as shown in FIG. 1B, to form a bump (plated film) 16 in the opening 14, the bump (plated film) 16 tends to grow faster on the downstream side of the flow of the plating solution than on the upstream side (this tendency is strongly affected by the properties of the plating solution used and, in certain cases depending on a type of the plating solution, the bump 16 grows rather slower on the downstream side). As shown in FIG. 1C, the surface 16a of the bump (plated film) 16 formed is highly inclined on its one side toward one direction along the flow direction of the plating solution.
When the substrate W shown in FIG. 1A is prepared and the surface of the substrate W is brought into contact with a plating solution, whose flow direction is reversed repeatedly, as shown in FIG. 2A, to form a bump (plated film) 16 in the opening 14, the surface 16b of the bump (plated film) 16 formed, though improved to some extent, has an arched profile, as shown in FIG. 2B. In order to avoid such drawbacks and flatten a surface of a plated film, it is necessary to perform plating of a substrate surface by bringing the substrate surface into contact with a plating solution whose flow direction can be switched among three or more directions.
When plating of a substrate surface is carried out by bringing the substrate surface into contact with a plating solution whose flow direction can be reversed, or switched among three or more directions, and when the reversal (switching) of the flow direction of the plating solution in a plating tank is performed by on-off control of an on-off valve, for example, a slight mistiming in opening/closing of the on-off valve could stop the flow of the plating solution, or conversely, instantaneously increase the flow rate (flow velocity) of the plating solution flowing into the plating tank. This may result in lowering of the plating performance when the plating performance depends on the intensity of the flow of the plating solution. The above phenomenon is virtually unavoidable if on/off control of an on-off valve is employed to reverse (switch) the flow direction of a plating solution in a plating tank.
For example, consider the case where a first plating solution supply system A and a second plating solution supply system B, each having an on-off valve to be on/off-controlled, are used, and plating solutions are supplied in orthogonal directions into a plating tank P alternately from the respective supply systems during plating, as shown in FIG. 3. The on-off valve of the first plating solution supply system A is turned on and the on-off valve of the second plating solution supply system B is turned off when supplying a plating solution into the plating tank P through the first plating solution supply system A. The on-off valve of the second plating solution supply system B is turned on and the on-off valve of the first plating solution supply system A is turned off when supplying a plating solution into the plating tank P through the second plating solution supply system B.
Upon switching from the first plating solution supply system A to the second plating solution supply system B, the operation of closing the on-off valve of the first plating solution supply system A must be performed simultaneously with the operation of opening the on-off valve of the second plating solution supply system B. If the on-off valve of the first plating solution supply system A is closed later, or the on-off valve of the second plating solution supply system B is opened earlier, then the flow rate (flow velocity) of the plating solution, flowing into the plating tank P, increases instantaneously, as shown in FIG. 4A. Conversely, if the on-off valve of the first plating solution supply system A is closed earlier, or the on-off valve of the second plating solution supply system B is opened later, then the flow rate (flow velocity) of the plating solution, flowing into the plating tank P, decreases instantaneously or becomes zero, as shown in FIG. 4B.
The applicant has proposed a plating apparatus and method which uses a plurality of inlet pipes and a plurality of outlet pipes, connected to a plating tank, and can arbitrarily switch the flow direction of a processing liquid in the plating tank by performing switching between the inlet pipes and between the outlet pipes (see patent documents 6 and 7).